Tightrope walking - or tightrope motocross riding, as rather awesomely seen here - may seem like an impossibly complex skill of athletic ability and audacity. But a new mathematical model reveals one trick to mastering this seemingly arcane art.

Harvard researchers have developed a model that seeks to put together all the forces, masses, angles, and velocities that go into the interactions between the person and the tightrope in order to find the optimal balancing conditions. They also considered how the person's sensory systems affect her ability to walk across the rope, particularly visual information and input from the balance centers in the inner ear. As ScienceNOW explains, the researchers were able to key in on the tightroping sweet spot:

In their calculations, they suggest that rapid information about falling provided by the inner ear is sufficient to help a rope walker maintain his or her balance. The team also discovered that a key feature affecting balance is the rope's sag. A tight rope with little sag makes quicker vibrations, whereas a loose rope with a lot of sag makes larger back-and-forth swings. Between these two challenging extremes exists a "sweet spot"-an optimal sag of about 3 feet where balancing is easiest.

The sag of a rope changes as a person walks along it, and it is greatest when the person is halfway across. A rope walker who finds the sweet spot can balance more easily because there, "all your sensory control information can be easily tuned to the dynamics of the rope," says study author Paolo Paoletti, an applied mathematician. "The time that you need to react coincides with the time that the rope makes one swing."

Tightrope walkers had actually already discovered that particular sweet spot after generations of trial and error, as most guidebooks will advise beginners to set about three to four feet worth of sag in their rope. For more, check out the whole story at ScienceNOW or the original paper at Journal of the Royal Society Interface.